Marine ecoregions
Encyclopedia
Marine ecoregions are areas of the sea identified and defined based on biogeographic characteristics. A more complete definition describes them as “Areas of relatively homogeneous species composition, clearly distinct from adjacent systems” dominated by “a small number of ecosystems and/or a distinct suite of oceanographic or topographic features”. Ecologically they “are strongly cohesive units, sufficiently large to encompass ecological or life history processes for most sedentary species.” A global classification of Marine Ecoregions of the World (MEOW) was devised by an international team, including major conservation organizations, academic institutions and intergovernmental organizations. The digital ecoregions layer is available for download as an ArcGIS Shapefile.

This system has a strong biogeographic basis, but was designed to aid in conservation activities for marine ecosystems. The Marine Ecoregions of the World classification defines 232 marine ecoregions (e.g. Adriatic Sea
Adriatic Sea
The Adriatic Sea is a body of water separating the Italian Peninsula from the Balkan peninsula, and the system of the Apennine Mountains from that of the Dinaric Alps and adjacent ranges...

, Cortezian, Ningaloo, Ross Sea
Ross Sea
The Ross Sea is a deep bay of the Southern Ocean in Antarctica between Victoria Land and Marie Byrd Land.-Description:The Ross Sea was discovered by James Ross in 1841. In the west of the Ross Sea is Ross Island with the Mt. Erebus volcano, in the east Roosevelt Island. The southern part is covered...

) for the coastal and shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...

 waters of the world. These form part of a nested system and are grouped into 62 provinces (e.g. the South China Sea
South China Sea
The South China Sea is a marginal sea that is part of the Pacific Ocean, encompassing an area from the Singapore and Malacca Straits to the Strait of Taiwan of around...

, Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...

, Central Indian Ocean Islands
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

) that, in turn, are grouped into 12 major realms. The latter are considered analogous to the eight terrestrial ecozones, represent large regions of the ocean basins: Arctic, Temperate Northern Atlantic, Temperate Northern Pacific, Tropical Atlantic, Western Indo-Pacific, Central Indo-Pacific, Eastern Indo-Pacific, Tropical Eastern Pacific, Temperate South America, Temperate Southern Africa, Temperate Australasia, Southern Ocean.

Other classifications of marine ecoregions or equivalent areas have been widely developed at national and regional levels, as well as a small number of global schemes. One of the most comprehensive early classifications was the system of 53 coastal provinces developed by Briggs in 1974. The near-global system of 64 large marine ecosystems
Large marine ecosystem
Large marine ecosystems are regions of the world's oceans, encompassing coastal areas from river basins and estuaries to the seaward boundaries of continental shelves and the outer margins of the major ocean current systems...

 has a partial biogeographic basis, while the World Wildlife Fund identified 43 priority marine ecoregions as part of it’s Global 200 efforts. Each of these systems, along with numerous regional biogeographic classifications, was used to inform the MEOW system. The WWF Global 200 work also identifies a number of major habitat types that correspond to the terrestrial biomes: polar, temperate shelves and seas, temperate upwelling, tropical upwelling, tropical coral, pelagic (trades and westerlies), abyssal, and hadal (ocean trench).
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